Using a gene array, we have identified that expression of Raf kinase inhibitor protein (RKIP) is down-regulated in prostate cancer metastases. RKIP inhibits JAK/STAT activation and Raf-mediated activation of MEK/ERK. Immunohistochemistry confirmed that RKIP is present in normal prostate and primary prostate tumors, but absent in prostate cancer metastases. Furthermore, we have demonstrated that transfection of a metastatic prostate cancer cell line with RKIP cDNA prevents metastasis in a murine model while having no effect on growth rate of the primary tumor and transfection of a non-metastatic prostate cancer cell line with antisense RKIP promotes metastasis. Taken together, these data lead us to hypothesize RKIP is a prostate cancer metastasis-suppressor gene, whose loss promotes metastasis through MEK/ERK and JAK/STAT. To test our hypothesis, we will perform the following specific aims: 1. Determine the extent of RKIP's metastasis suppressor activity in vivo. Using several novel prostate cancer cell lines we will determine the effect of modulating RKIP levels on metastasis in murine models. 2. Identify the cellular mechanism(s) through which RKIP dysregulation promotes metastasis. We will evaluate the effect of manipulating RKIP levels on pro-metastatic parameters including angiogenesis, endothelial adhesion and invasiveness. Once we identify a target molecule based on these in vitro studies we will use inhibitors in vivo to determine if blocking these activities inhibits loss of RKIP-mediated metastasis. 3.Determine the signaling pathways through which decreased RKIP expression mediates metastasis. We will evaluate the effects of modulating the activities of the JAK/STAT and MEK signaling pathways on in vitro parameters including invasion, proliferation and apoptosis. Subsequently, we will determine the effect on establishment of metastases in vivo. Furthermore, we will determine if any pro-metastatic cellular phenotypes identified in Aim 2 are modulated by these signaling pathways. when completed, we hope this work will lead to a better understanding of the mechanisms through which RKIP suppresses metastasis and hopefully identify specific targets to inhibit metastasis. [unreadable] [unreadable]